1. Field of the Invention
The present invention generally relates to an information recording/reproducing method and, more particularly, to an information recording/reproducing method capable of accessing a desired track on a recording medium such as an optical card at high speed.
2. Description of the Related Art
Recently, information recording/reproducing systems using various types of recording media have been developed. They have been used in a variety of fields.
In such information recording/reproducing systems, optical cards start to attract a great deal of attention. This is because an optical card has a storage capacity several thousands to ten thousands times larger than that of a magnetic card. Similar to an optical disk, such an optical card is not generally rewritable. An optical card, however, has a large storage capacity of 1 to 2 Mbytes. For this reason, a wide variety of applications of optical cards, e.g., banknotes, portable road maps, and pre-paid cards used for shopping, have been proposed.
Such conventional optical cards are disclosed in, e.g., Published Unexamined Japanese Patent Application No. 63-37876. In one type of optical card, an ID portion on which the address information of each track is recorded is formed on only one end portion of a corresponding one of a plurality of parallel tracks (to be referred to as a single-side ID optical card hereinafter). In another type of optical card, ID portions are formed on the two ends of each of tracks (to be referred to as a double-side ID optical card hereinafter).
In an optical card of this type, recording/reproducing of data and reading of ID portions, sector marks, and the like are performed by relatively moving the optical card in an optical beam from a recording/reproducing optical head in a direction parallel to the tracks on the optical card. A target track is accessed by performing a combination of coarse-accessing and track-jumping operations in accordance with commands from a controller. In a coarse-accessing operation, coarse positioning is performed by moving the overall optical head having an objective lens by means of a linear moving mechanism in a direction perpendicular to each track on the optical card, and simultaneously detecting the position of the moving optical head by means of a position detecting section. In a track-jumping operation, the object lens is moved every track pitch by means of a tracking drive means.
In a conventional system, therefore, when a single-side ID optical card 1 shown in FIG. 6 is used, a target track is accessed in accordance with a flow chart shown in FIG. 7. Note that in the optical card 1 shown in FIG. 6, ID portions 4 on which the address information of the respective track are recorded are formed, in correspondence with the tracks, on only one end portion of an optical recording portion 3 having a plurality of parallel tracks 2, and a data portion 5 is formed between the ID portion 4 and the other end portion of the optical recording portion 3. The ID portion 4 can be properly read by reading the optical card 1 from a right end portion to the left.
A conventional accessing method with respect to the single-side ID optical card 1 will be described below with reference to a view showing the locus of a light beam directed onto the optical card in FIGS. 6 and a flow chart in FIG. 7.
Referring to FIG. 6, assume that the optical card 1 is stopped, a recording/reproducing light beam is directed to an end position S1 on a side opposite to the ID portion 4, and the address of a corresponding track has already been read. A controller moves the optical card 1 in a direction parallel to the track to direct the light beam to an end position S2 on the opposite side to the end position S1 (step S11). The controller calculates a difference D between the address of a target track and that of the current track (step S12), and checks whether an absolute value .vertline.D.vertline. of the difference D is smaller than a predetermined value (step S13). If .vertline.D.vertline.&lt;a, the target track can be accessed in a shorter period of time by repeating a track-jumping operation than by performing a coarse-accessing operation of moving the overall optical head. In this case, therefore, the controller does not perform a coarse-accessing operation but performs a track-jumping operation by an amount corresponding to the track difference D (step S14). Note that the predetermined value a is normally set to be about 4 to 10. If .vertline.D.vertline.&gt;a, the controller moves the overall optical head by a distance corresponding to the track difference D to perform a coarse-accessing operation (step S15). Reference symbol S3 in FIG. 6 denotes the directed position of the light beam after the movement described above.
Subsequently, the controller moves the optical card 1 in the track direction (step S16), and simultaneously reads the address, of the corresponding track, recorded on the ID portion 4 to detect the address of the track after the movement (step S17). At the same time, the controller checks whether the detected address corresponds to the target track (step S18). In this case, if the access is made by a track-jumping operation, the detected address coincides with that of the target track in most cases. However, if the access is made by coarse-accessing operation, the detected address does not often coincide with that of the target track. If they do not coincide with each other, the controller immediately stops the movement of the optical card 1 (step S19), and directs the light beam to a position S4. Thereafter, the controller calculates the difference D between the address of the current track and that of the target track in the same manner as described above (step S20) to perform access control again. In this case, since the position S4 to which the light beam is directed is located relatively near the target track regardless of whether the first accessing operation is performed by track jumping or coarse accessing, .vertline.D.vertline.&gt;a. For this reason, the controller performs track-jumping operation by an amount corresponding to the difference D (step S21), thus directing the light beam to a position S5. Subsequently, the controller moves the optical card 1 in the opposite direction to direct the light beam to an end position S6 on the side of the ID portion 4 of the optical card 1 (step S22). Lastly, the controller drives the optical card 1 from the position S6 (step S23), and reads the address of the corresponding track in the ID portion 4 again (step S17). If the read address coincides with the address of the target track (step S18), the controller performs a read or write operation with respect to the data portion 5.
In contrast to this, when a double-side ID optical card is used, ID portions are arranged on the two end portions of each track. Therefore, the controller immediately performs a coarse-accessing operation or a track-jumping operation to start accessing to a target track, while omitting step S11 in the above-described accessing operation of the single-side ID optical card, regardless of whether the light beam is directed to one end or the other end.
As is apparent from the above description, in the conventional access method for a single-side ID optical card, if a light beam is located at an end portion on the opposite side of the ID portion, the optical card is moved to position the light beam to an end portion near the ID portion in the first place. Since such movement requires an extra time, the access time is inevitably prolonged.
An information recording/reproducing system using such a single-side ID recording medium (optical card), therefore, cannot access to a desired track at high speed. This interferes with a high-speed read/write operation.